Conventional optical biometric devices can be used to detect and recognize faces, sounds, irises, retinas or fingerprints. Taking the fingerprint identification device as an example, the fingerprint identification device can be applied to an electronic product (such as a smart phone or a tablet computer) to identify the user.
In existing electronic products, a light beam generated by a display panel is generally used as a sensing light source for fingerprint recognition. The aforementioned display panel is, for example, an organic light emitting diode display panel. In the conventional fingerprint identification device applied to electronic products, when a light transmitting plate located at the outermost side thereof is pressed with a finger of a user, the light beam generated by the display panel is projected onto the light transmitting plate. After the total reflection of the interface between the light transmitting plate and the environmental medium (i.e., the outer surface of the light transmitting plate) is generated, the light beam is then received by the image sensor.
Since the finger has a plurality of irregular ridges and valleys, when the user places the finger on the light transmitting element, the ridges will contact the light transmitting element, while the valleys will not contact the light transmitting element. Therefore, the ridges contacting the light transmitting element may destroy the total reflection of the light beam in the light transmitting element, while the valleys not contacting the light transmitting element will not affect the total reflection of the light beam, so that the fingerprint pattern captured by the image sensor has dark lines corresponding to the ridges and bright lines corresponding to the valleys. Subsequently, the fingerprint pattern captured by the image sensor is processed by the image processor to further determine the identity of the user.
However, when the conventional fingerprint identification device is integrated with the thin film transistor liquid crystal display, the light beam generated by the backlight module of the thin film transistor liquid crystal display is diffused by the diffusion sheet before being projected onto the light transmitting plate. In this way, when the fingerprint image is captured, the light beam projected onto the light transmitting plate is relatively uneven, and the obtained fingerprint image is relatively blurred, which affects the accuracy of the identification.
A light-emitting element is additionally provided in the related art to generate a light beam for recognizing the fingerprint. After the light beam generated by the light-emitting element enters the light transmitting element, the light beam is totally reflected in the light transmitting member multiple times. When the user presses the outer surface of the light transmitting element with a finger, the image sensor can capture the fingerprint pattern.
However, contaminants such as particles or dust may easily be attached onto the outer surface of the light transmitting element, so that the total reflection of the light beam in the light transmitting element is broken. Therefore, before the beam is transmitted to the position where the finger is pressed, a part of the beam is lost, thereby affecting the image quality of the image sensor.